Messages in this thread | | | Date | Sat, 18 Apr 2015 10:01:47 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [tpmdd-devel] [RFC PATCH 1/2] tee: generic TEE subsystem |
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On Fri, Apr 17, 2015 at 10:30:54AM -0600, Jason Gunthorpe wrote: > On Fri, Apr 17, 2015 at 09:50:56AM +0200, Jens Wiklander wrote: > > + teedev = devm_kzalloc(dev, sizeof(*teedev), GFP_KERNEL); > [..] > > + rc = misc_register(&teedev->miscdev); > [..] > > +void tee_unregister(struct tee_device *teedev) > > +{ > [..] > > + misc_deregister(&teedev->miscdev); > > +} > [..] > >+static int optee_remove(struct platform_device *pdev) > >+{ > >+ tee_unregister(optee->teedev); > > Isn't that a potential use after free? AFAIK misc_deregister does not > guarentee the miscdev will no longer be accessed after it returns, and > the devm will free it after optee_remove returns. > > Memory backing a stuct device needs to be freed via the release > function.
Out of interest, which struct device are you talking about here?
struct tee_device contains two things - a struct device _pointer_ to the device passed into the registration function, and a miscdev.
A miscdev contains two struct device _pointers_ - a pointer to the parent device, and a pointer to the char class device. As both of these are pointers, freeing struct tee_device does not free the memory underlying any device structure.
What does need to be taken care of is that unbinding the parent device may cause an already-open user of the userspace interface to dereference the memory which was freed. Tying this to the lifetime of a struct device doesn't seem right.
I would suggest adding a kref to struct tee_device and use that to manage the lifetime of that structure - incrementing the refcount on fops->open and dropping it at fops->release time, so that the struct is automatically freed when the last user closes the miscdev after the device has been unbound. You should probably also have a flag to indicate that the device is no longer present too to prevent further userspace IO.
It would be nice if miscdev provided help with this...
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